Update release notes

Author: fredericDelaporte

releasenotes.txt

@@ -3,7 +3,7 @@
 
 Release notes - NHibernate - Version 5.3.0
 
-203 issues were resolved in this release.
+204 issues were resolved in this release.
 
     ##### Possible Breaking Changes #####
         * A distributed cache may hold conflicting timestamps after upgrade for as much as twelve hours.
@@ -135,6 +135,7 @@ Release notes - NHibernate - Version 5.3.0
 
 ** Improvement
 
+   * #2394 Optimize PersistentGenericSet snapshot
    * #2352 Improve performance of ReflectHelper.GetMethod/Definition
    * #2350 Optimize LINQ batch item processing for queries with overridden result type
    * #2316 Add multiple arguments support for ISQLFunction